We developed monoclonal antibodies to CD209 and CD163 to provide a more direct way to identify the major myeloid population of dendritic cells in blood (bDC) and determine their relation to monocyte derived DC (MoDC) and monocyte derived macrophages (MoMΦ). Initial studies showed CD209 and CD163 are co-expressed on bDC, MoDC, and MoMΦ. Further comparative studies were conducted to determine the pattern of expression of CD209 and CD163 with other mAbs used to characterize myeloid mononuclear cells in blood: CD14, CD16, CD21, and CD205. The analysis revealed the CD209+ population is comprised of multiple subsets that vary in expression of CD14, CD16, CD21, CD163, and CD205. Further analysis demonstrated that the subsets can be divided further by comparing expression of CD14, CD16, and CD163. The results clearly demonstrate myeloid population of mononuclear cells previously defined as monocytes in blood, based on expression of CD14, is phenotypically heterogeneous. In goats and sheep, CD163 is a more definitive marker than CD14 for identifying all mononuclear cells in blood. Further studies are needed to determine the function of each subset.